Marion police initiated a “lock out” at Linn-Mar High School on Monday afternoon after a concerned parent informed authorities of a disturbing image on Snapchat. Police Chief Joseph McHale said the image depicted a weapon near the school, but he was unable to disclose the type of weapon.

Following the lockout, police said a juvenile was arrested on charges of false reporting, a serious misdemeanor, and turned the matter over to the Linn County Attorney’s Office Juvenile Division.

McHale said police contacted the school just before 1 p.m. and, out of an “abundance of caution,” they instructed the school to initiate the lockout.

During a lockout, all exterior doors are locked and no one is let in, according to a statement from the school.

Within 20 minutes, McHale said investigators located the parties involved and determined the school was not threatened.

Though classes might have experienced a slight disruption during the lockout, McHale said the procedure is the “least disruptive” form of lockdown, as it allows the school to operate normally while keeping people from entering the building.

The lockout ended at about 1:15 p.m., according to school officials.

Marion police said the investigation is ongoing and applicable charges are being reviewed.